Continuous development of wireless communications technologies poses higher requirements on a rate of wireless communications, and wireless communications protocols and technologies keep developing. To meet requirements on a better single-user peak rate and a higher system capacity, a direct method is increasing a system transmission bandwidth. Therefore, a technology for increasing the transmission bandwidth is introduced for a Long Term Evolution Advanced (English: Long Term Evolution Advanced, LTE-A for short) system, that is, a carrier aggregation (English: Carrier Aggregation, CA for short) technology.
The CA technology can aggregate at least two component carriers (English: Component Carrier, CC for short), to provide a higher transmission bandwidth, so that an uplink transmission rate and a downlink transmission rate are effectively improved. For example, it is assumed that a bandwidth of each CC is 20 MHz. If five CCs are aggregated, a transmission bandwidth of 100 MHz can be achieved.
To implement CA on a terminal device side, when a CA combination manner cannot be implemented by using a diplexer (Diplexer) for a CA combination of very closely contiguous communications frequency bands, there are generally two other implementations. One implementation is using a quadruplexer or a sextaplexer. The quadruplexer has four input ports and one output port. The four input ports are connected to two transmit channels and two receive channels, respectively. Therefore, carriers on two frequency bands can operate simultaneously, so that CA of two CCs can be implemented. Similarly, the sextaplexer has six input ports and one output port. The six input ports are connected to three transmit channels and three receive channels, respectively. Therefore, carriers on three frequency bands can operate simultaneously, so that CA of three CCs can be implemented.
The other implementation is connecting at least two duplexers (Duplexer). Each duplexer can receive and transmit signals on one frequency band. Therefore, if at least two duplexers are simultaneously connected, CA of at least two CCs can be implemented.
In the previous CA implementation, frequency bands are closely contiguous. Therefore, to eliminate interference between the frequency bands, a design is relatively difficult. In the latter CA implementation, a design of the duplexer itself is difficult, and a relatively great insertion loss of the duplexer affects radio frequency performance. As a result, in the prior art, it is difficult to design a radio frequency front end for implementing CA.